3.6. Additional Information on XML Schema
Although XML schemas have been standardized, the area of validation is still a
research subject and alternatives have been proposed: see
[29]
for a comparison between some of them. Interesting links are being made with relational
database models
[34]
in order to build on its strong theoretical background. Schemas and the validation
process are being formalized
[13].
We have only skimmed over the subject of validation of XML files but the same
essential ideas apply throughout. On top of the official and informal information
available at
http://www.w3.org/xml/Schema, some good sources of information and
interesting tutorials can be found in the following resources:
-
http://www.XML.com
- is maintained by the O'Reilly editor with many excerpts from their
books.
-
http://www.XML.org
- is a market-oriented site with interesting files in the
resources
section.
-
http://www.mulberrytech.com/quickref/XMLquickref.pdf
- a very useful XML Syntax Quick Reference Sheet (US letter
size).
-
http://www.xfront.com/xml-schema.html
- a complete XML Schema tutorial in roughly 150 Microsoft Powerpoint
slides with example source code
-
http://www.xfront.com/schematron/
- Tutorial and links for Schematron
-
http://www.xmlspy.com
- XMLSpy is a commercial XML editor on the Microsoft Windows
platform, with a powerful structure editor and internal validation and
real-type suggestions of allowable elements attributes (strangely, these
suggestions are not adequate in the text view i.e.
the mode in which XML tags are explicitely typed). It is easy to
switch between the text view and the structural view of the editor.
There is also a good stylesheet designer module (Stylevision) to create stylesheet
transformations interactively and graphically. These transformations can
then be used as a basis for what is called the
authentic view which can effectively hide the
XML tags from the user of an XML document.
-
http://www.oxygenxml.com/
- <oXygen/>
is an XML editor for Microsoft Windows, Linux, MacOS X and Solaris.
Real-time valid suggestions are offered in the text view. Validation can
be done within the editor. Stylesheets transformations can be displayed
in a window of the editor. It also features table and tree editing modes
and a similar graphical output of a schema to what is provided by
XMLSpy. Unfortunately, it is not possible to edit the schema
graphically. It is one of the few XML editors that also offers
real-time Schematron validation. For XML files, there is also an
author mode which allows a
tagless XML editing of the file
directly from the rendered version through Cascading Style Sheets. As
the formatting allowed with CSS is less powerful than what is possible
with StyleSheets, this mode does not allow a full rendering like the
authentic mode of XMLSpy but it has the
advantages of being based on open standards. But for documented
oriented XML files such as the ones written in DocBook or XHTML,
this mode is quite convenient and user friendly.
-
http://www.thaiopensource.com/nxml-mode/
- nXML
mode in Emacs
[19]
offers real-time valid suggestions for editing XML files in text
mode only when their schema is written in RELAX NG. Trang can be used for
translating an XML Schema or a DTD into RELAX NG.